This invention generally relates to mechanical refiners for lignocellulosic materials, and more specifically to a method and system for changing refiner plate segments in such a refiner.
Refiner plate segments are a critical component of the refining equipment. They are also a wear part that requires changing on a regular basis, in order to maintain the refining performance over time. For example, a typical circle of refiner plates is composed of anywhere between three (3) and twenty-four (24) equally-sized segments, which together form a circle. At every refiner plate change, all segments are removed, the mounting surface (that is, the surface of the rotor or stator disk) are cleaned, and the new segments must be installed one-by-one, shimmed to keep equal spacing and torqued properly.
Refiners usually have two circles of plates running opposite each other, or in case of twin refiners, they have four circles of plates (including a double-sided rotor). The refiner may be made with one rotor facing one stator (a rotating disk facing a stationary disk), or two opposite counter-rotating rotors.
The time required to change refiner plates segment-by-segment varies with the refiner type, but typically ranges from three (3) to twelve (12) hours, and generally requires a large number of workers to handle all the parts. It can be a long and expensive process, during which the mills are losing production time.
Some refiners are equipped with refiner plate holders. Those plate holders may be thick disks (usually on-inch (1″—25 mm) thick or more) onto which the individual refiner plate segments can be pre-mounted while the refiner is still in operation. When a refiner plate change is needed, the plate holder with the worn plates is removed then replaced with the plate holder with the new refiner plate segments. This can be done much faster and may require only one (1) to two (2) hours stop time as well as fewer workers. With this technology, the refiner plate segments are typically mounted solidly onto the plate holder, and the plate holder itself may be attached to the disk (which may be either a rotor or a stator disk). Due to the potential for very high forces in the refining process, this may require a thick plate holder acting as the binder between the disk and the rotor plate segments.
A limitation of the existing refiner plate holders is that they may require a certain minimum thickness in order to be used safely. Refiner plate segments may also have a minimum thickness requirement, allowing bolts to fasten them to the disk or to the plate holder. Generally, this minimum thickness may be in the region of an inch to one and a half inches (1.0-1.5″—25 mm to 38 mm), depending on the fastening method. The plate holder may also need to be at least one inch (1″—25 mm) thick (but may be thicker in some circumstances) in order to take the required stresses to safely retain plates on the holders. Altogether, there may be a minimum thickness requirement for the assembly that is greater than two inches (2″—50 mm) thick for using traditional plate holders. Many refiners do not have enough clearance to allow for the use of such a thick assembly. It may be possible to offset this requirement by making modifications to the refiner itself. Those modifications can be very expensive, because a new rotor disk may be necessary. Those modifications may also be irreversible.
It will be appreciated that the use of refiner plate holders in refiners is well-known. But existing refiners using plate holders are either designed to use these existing, well-known plate holders or must be modified—oftentimes significantly—in order to allow for the use of traditional plate holders. Known plate configurations may relate to sound absorption, as described in U.S. Patent Application Publication No. 2002/0166912 A1 to Schneid. Any retrofitting can increase the space requirement between the refining disks.